1. Field of the Invention
The present invention relates to a switching device, and, more particularly, to a switching device that is easy to operate and is so small as to be disposed in the housing of an electric apparatus such as a copying machine, a printer, or a personal computer, and can be used for at least either leakage prevention or excess voltage prevention. The present invention also relates to such an electric apparatus.
2. Description of the Related Art
There have been ground-fault interrupters as domestic wiring devices for detecting and shutting off leakage in domestic wirings (see Japanese Laid-Open Patent Application Nos. 2000-261953, 2001-023501, and 2001-006515). The structures and forms of the conventional ground-fault interrupters are standardized in accordance with the JIS (Japanese Industrial Standards), and the necessary components are housed in standardized housings.
For example, the ground-fault interrupter that is disclosed in Japanese Laid-Open Patent Application No. 5-334953 has a housing that is formed with a main casing and a main cover. This housing contains a zero phase current transformer and an overcurrent transformer that detects leakage and overcurrent in the main circuit, an open-close mechanism unit that opens and closes the main circuit, trip coils that drive the open-close mechanism unit, and the like. One of the trip coils is employed to eliminate leakage, while the other one of the trip coils is employed to eliminate overcurrent. Further, a leakage display device that displays each occasion of leakage elimination in conjunction with the trip coil for eliminating leakage is disposed in the housing in such a manner that each occasion of leakage elimination can be recognized through the housing. In this manner, this ground-fault interrupter has a closed structure.
In such a conventional ground-fault interrupter, the open-close mechanism unit that opens and closes the main circuit is opened by the trip coils, and is closed through a handle that is manually operated after leakage or overcurrent is eliminated. However, priority is put on the opening operation with the trip coils, and the open-close mechanism unit is designed to be accommodated in the housing.
Japanese Laid-Open Patent Application No. 11-299082 discloses a ground-fault interrupter device that includes not only a leakage detector and an excess voltage detector, but also a means of releasing a load from the power source based on the output of either of the leakage detector and the excess voltage detector. With this ground-fault interrupter device, a load can be released from the power source not only when there is leakage but also when excess voltage is detected. Thus, load damage due to abnormal voltage or excess voltage can be prevented.
In each of the above conventional ground-fault interrupters, however, all the necessary components are contained in the housing standardized as a domestic wiring device in accordance with the JIS. Therefore, in a case where such a ground-fault interrupter is employed in an electric apparatus such as a copying machine, a printer, or a personal computer, it is difficult to secure a sufficient ground space in the apparatus. If a sufficient ground space is secured, the apparatus becomes large in size.
Also, the ground-fault interrupter disclosed in Japanese Laid-Open Patent Application No. 5-334953 has the function of detecting leakage and the function of detecting overcurrent. The components that execute those functions are accommodated in the JIS housing, and are hermetically closed by the housing. As a result, the inner structure becomes complicated, and the product becomes expensive. In a case where a ground-fault interrupter having such a housing is disposed in an apparatus, there are two housings existing in one structure. Due to heat generation from the inner components, the temperature in the housing of the ground-fault interrupter becomes higher, resulting in a decrease in detection accuracy.
Further, since the open-close mechanism unit has priority on the opening operation with the trip coils and is designed to be contained in a housing, the handle to open the main circuit of the open-close mechanism unit is not lightly moved, resulting in poor operability and usability.
As for the ground-fault interrupter device disclosed in Japanese Laid-Open Patent Application No. 11-299082, the control circuit is not protected, because operating current is supplied to the control circuit even after the load is released from the power source. Even if excess voltage is detected, the excess voltage is supplied to the control circuit. Further, in this structure, a short-circuit relay is constantly used. In a case where the excess voltage is not eliminated when the main power supply is switched back on, a shutoff operation needs to be performed again. The repetitive shutoff operation might have adverse influence on the load.
Also, as a smoothing capacitor is used to monitor excess voltage so as to increase the detection accuracy, there is a decrease in the accuracy of impulse excess voltage detection. Since the operating power is supplied separately to the leakage detector and the excess voltage detector, a large quantity of standby power is required.